The investigators propose to investigate the degree to which volatile organic compounds such as trichloroethylene and vinyl chloride are degraded in unsaturated soil systems amended with gas-phase nutrients required by methanotrophic and ammonia-oxidizing bacteria. The work conditions will be designed to promote the unique cometabolic capabilities of methanotrophs and ammonia oxidizers taking advantage of the relative ease of transporting gas-phase nutrients through the vadose zone. Nutrient amendments to soil columns would take the form of methane and ammonia or alternate gaseous sources of nitrogen. Experiments will be conducted at different scales from microcosms to large lysimeters. A mathematical model will be developed to describe the results and to predict the fate and mass transport in the vadose zone. Operating conditions for the lysimeter studies will be selected on the basis of the model.